This invention is concerned with automotive electronic control systems, and in particular with increasing the immunity of such systems to electromagnetic interference.
The term "automotive electronic control systems" as used herein includes, for example, electronically controlled braking systems (including "brake-by-wire" systems in which electrical signals produced by movement or position of a brake control element for example a brake pedal are effective to control brake operation, and/or anti-lock braking systems of electronic type), electronic engine management systems, suspension systems in which at least some suspension movement(s) or characteristic(s) is or are electronically controlled, and electronic traction control systems (in which wheelspin on low friction surfaces is prevented or reduced by electronic control of the vehicle engine and/or brakes).
Customarily such automotive electronic control systems comprise control circuits ("controllers") of electronic logic type, typically comprising microprocessors or other computing means, which provide apparatus-controlling electrical output signals in response to the level or levels of one or more electrical input signals. The input signals may be derived from a sensor which senses a relevant parameter for movement or position of a brake control element or a wheel speed sensor or an engine or transmission or ambient environment parameter or a suspension position parameter.
The operation of such controllers can, however, be particularly susceptible to spurious or inappropriate currents and voltages induced in wires carrying input and/or output signals of the controller and/or in the controller itself by unwanted radiated electromagnetic interference arising, for example, from nearby other vehicles and/or from other sources, and this susceptibility can have serious operational and safety consequences.
Because of constraints imposed by manufacturing methods and unit cost, it has not been commercially acceptable to attempt to increase the immunity of such controllers to such interference by the use of high insertion loss input filters, screened cables or enclosed metal housings.